36 THE NEW PHYSIOLOGY. 



ing quality and amounts of the substances we eat and 

 drink, and which pass through our blood, can this physio- 

 logical environment be at all constant ? I will leave 

 this question for the moment and meanwhile follow 

 up another path in the analysis. 



The actual faint alkalinity of the blood and its power 

 of carrying carbon dioxide in readily dissociable chemical 

 combination depend on the presence in the blood in 

 certain amounts, and in a certain mutual balance, of a 

 number of substances ; and it is clear that, if an alteration 

 in this balance occurred, the degree of alkalinity in both 

 arterial blood and tissues would also be very seriously 

 disturbed unless compensated by considerable variations 

 in the alveolar carbon dioxide percentage and the rate 

 of circulation. Now, during rest under normal conditions 

 of health such variations do not occur to any extent 

 which is appreciable except by unusually exact measure- 

 ment, or which is more than a very temporary or passing 

 change. Among the many exact regulations which exact 

 quantitative research is rapidly revealing within the 

 living body none is more remarkable than the exactitude 

 with which the capacity of the blood for carrying carbon 

 dioxide is regulated. Such variations as ordinarily 

 occur are within the limits of error of the most exact 

 methods which we have been able to devise for the 

 purpose. The balance can, it is true, be upset tem- 

 porarily by artificial means ; but in a very short time 

 it rights itself. 



The salts of the blood, on which this balance mainly 

 depends, must, in the long run, be regulated by the 

 balance between absorption from the intestine and 

 excretion by the kidneys. So far as we know, all soluble 



